Hermetically sealed distribution transformer



T. H. KEOGH Oct. 21, 1969 HERMETICALLY SEALED DISTRIBUTION TRANSFORMER 2 Sheets-Sheet Filed Dec. :3, 1967 United States Patent US. Cl. 33665 14 Claims ABSTRACT OF THE DISCLOSURE A hermetically sealed distribution transformer has a tank which exhibits maximum strength against deformation caused by internal pressure variations formed by a circuluar sidewall member welded at its open upper and lower ends to outwardly domed cover and bottom members 11 and 12. The tank encloses a transformer core and coil assembly 21 held together by a frame including upper and lower pans 29 and 30' locked by end straps 32. The central portion of the cover and bottom members 11 and 12 are stayed and rigidly secured to the frame by threaded studs 52 and 58 integral with plates 53 and 59 disposed beneath the pans 29 and 30 and extending through apertures in spacers 55 and 60 and engaging nuts 56 and 61 on the cover and bottom members. The interior of the tank is filled with a dielectric liquid 51 and is under negative pressure when the transformer is out of service so that no positive internal pressure is exerted against the walls of the tank during operation, thereby minimizing flexure of the tank walls due to pressure changes and permitting the transformer to be handled in any position without danger of air being entrapped in the windings.

This invention relates to stationary induction apparatus and in particular to hermetically sealed distribution transformers.

Distribution transformers often fail electrically due to deterioration of the transformer oil caused by entrance of moisture and other contaminants into the interior of the tank at the gasketed joint for the cover or the hand hole cover. Further, distribution transformers are larger and heavier than necessary because the tank is considerably taller and wider than the core and coil assembly and is filled with oil to a level above the core and coil assembly and has a cushion of air above the oil to compensate for expansion and contraction of the oil with temperature changes during operation. The cushion of air requires that transformer tank always be maintained in an upright position to prevent air from being trapped in the windings wherein it may cause failure during service. Hermetically sealed distribution transformers are known wherein the tank is permanently welded closed to prevent entrance of moisture and other contaminants, but such transformers are not entirely satisfactory in that the tank walls continuously flex due to expansion and contraction of the oil with temperature, and such continuous flexing can result in fatigue of the metal of the tank. Known hermetically sealed distribution transformers necessitate a pallet for fork truck handling and have spaced vertical cooling flanges with a flat surface therebetween which form a collecting place for dirt and corrosive material and a possible location for bird nests. Further, the low voltage bushings of such known hermetically sealed transformers .are located between the vertical flanges at three different distances from the pole in a location which makes connection thereto awkward and results in an unsightly drop arrangement.

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It is an object of the invention to provide an improved hermetically sealed distribution transformer which is approximately 35 percent smaller and 25 percent lighter in weight than conventional distribution transformers of equal rating and which can be stored and shipped in any convenient position and handled without danger of air being entrapped in the windings. Another object is to provide such an improved transformer which does not require a pallet for fork truck handling.

It is a further object of the invention to provide improved distribution transformer which permits mounting on horizontal poles while at a central location without danger of air being trapped in the windings, then trucked to the field and raised quickly to the vertical, thereby allowing quick and easy installation.

Another object of the invention is to provide an improved hermetically sealed distribution transformer having an arrangement of secondary bushings equally spaced from the pole which speeds installation, adds to polehngging compactness, results in a symmetrical drop arrangement, and permits the pole to be shorter than those utilized with conventional transformers.

Still another object is to provide an improved distribution transformer wherein the bushing height is considerably reduced in comparison to prior art transformers.

A still further object of the invention is to provide a hermetically sealed distribution transformer which minimizes flexing due to pressure changes within the tank and eliminates the danger of fatigue of the metal of the tank walls due to continuous flexing as a result of expansion and contraction of the oil.

Another object of the invention is to provide an improved permanently sealed distribution transformer wherein the maximum internal tank pressure caused by thermal expansion of the oil is limited.

These and other objects and advantages of the invention will be more readily apparent from the following detailed description when considered in conjunction with the accompanying drawing wherein:

FIG. 1 is a cross section view through a distribution transformer embodying the invention;

FIG. 2 is a plan view of the transformer of FIG. 1 with a portion of the cover and a portion of the top pan of the frame broken away to illustrate the internal construction;

FIG. 3 is a bottom view of the transformer of FIG. 1;

FIG. 4 is an enlarged view taken along line IVIV of FIG. 2;

FIG. 5 is an enlarged view taken along line VV of FIG. 3; and

FIG. 6 is an enlarged cross section view through one of the low voltage bushings taken along line VI-VI of FIG. 3.

Referring to the drawing, the hermetically sealed pole type distribution transformer of the invention has an aesthetically appealing round tank including a cylindrical shell 10 defining the tank sidewall jointed by welding at its upper open end to a circular cover 11 and at its open lower end to a circular tank bottom member 12. A U-shaped hanger bracket 15 for mounting the transformer on a pole is welded to shell 10 and extends below the tank bottom member 12 where it acts as a foot which cooperates with a depending foot 16 welded to tank bottom member 12 at a diametrically opposite'position from bracket 15 to provide means for supporting the transformer which permit fork truck handling without a pallet. Circular cover 11 is outwardly domed, i.e., convex, and has a depending circumferential flange 17 surrounding the upper end of, and welded to, cylindrical shell 10. Bottom tank member 12 is also outwardly domed, i.e., convex, and has a depending peripheral flange 19 which 3 fits within the open lower end of, and is welded to, cylindrical shell 10.

The transformer core and coil assembly 21 is of conventional construction and may include a pair of backto-back, closed, generally rectangular magnetic cores 22 having laminations 23 (see FIG. 2) of grain oriented magnetic steel linked with a transformer coil 26 having radially inner and radially outer low voltage winding sections 27 (only the latter being shown in FIG. 2) of aluminum strip conductor having a width equal to the axial length of the coil with a high voltage winding section wound from enamel insulated wire disposed between the inner and outer low voltage sections 27. The frame for the core and coil assembly 21 includes hollow upper and lower pans 29 and 30 respectively which embrace the back-to-back magnetic cores 22 at the upper and lower ends thereof and are locked together by heavy metallic end straps 32. The lower portions of the end straps 32 are secured to the lower pan 30, and the end straps 32 protrude through openings in the upper pan 29 and are bent over, while the pans 29 and 30 are pressed together, to lock the assembly together. Three low voltage insulating bushings 33 are secured in spaced apart relation to bottom tank member 12. Each bushing 33 may include a threaded hexagonal conductor stud 34 molded axially of a cylindrical body member 35 of suitable insulating material such as epoxy resin. Body member 35 may have a circumferential flange 36 internal of the tank and may also have external threads engaged within an internally threaded metallic ring 38 welded to tank bottom member 12, and body member 35 may be secured to ring 38 by suitable means such as cement. An eye terminal 39 crimped to a secondary lead 40 from low voltage winding 27 may fit over the threaded end of conductor stud 34 internal of the tank and be secured thereto by a nut 41 engaging the threads on stud 34. An eyebolt terminal 42 is bolted to conductor stud 34 by a socket head screw 43 engaged within a tapped hole 44 in the end of conductor stud 34 external of the tank. The base of eyebolt terminal 42 has a twelve point socket which fits over hexagonal conductor sutd 34 and permits indexing within seven and one-half degrees of any desired position. The secondary bushings 33 are equidistant from the pole and exit from the bottom of the tank immediately adjacent the pole where they shorten and facilitate installation of a symmetrical arrangement of secondary distribution leads (not shown) and permit use of poles which are considerably shorter than those on which conventional pole type distribution transformers are mounted.

One or more high voltage bushings 46 are mounted on cover 11 and may comprise a short length of unshielded high voltage cable 47 having insulation of suitable voltage rating molded axially within a bushing body member 48 cast of suitable insulation such as epoxy resin. Body member 48 may be generally of inverted conical shape and have a depending circumferential flange 49 spaced radially from its axial portion and having internal threads which engage external threads on a metallic pipe fitting 50 welded on cover 11. The conductor of cable length 47 is connected internally of the tank to a lead from the high voltage winding. The lower end of bushing body member 48 extends into the transformer oil 51 filling the tank, and the depending flange 49 extends creep distance downwardly externally of the tank and upwardly internally thereof, and both features contribute toward reduction of the external height of the high voltage bushing 46.

Both cover 11 and tank bottom member 12 are outwardly domed and stayed by the core and coil assembly 21 so that the tank walls exhibit virtually no deformation or flexing due to internal pressure changes within the tank. A threaded stud 52 (see FIG. 4) welded to a plate 53 disposed beneath upper pan 29 extends upwardly through the axial opening in an annular metallic spacer 55, positioned between cover 11 and upper pan 29. Stud 52 is welded to eyenut 56 after assembly to prevent leakage of oil from the tank. Stud 52 transmits the lifting force exerted on eyenut 56 directly to the core and coil assembly 21 and further rigidly connects cover 11 to the upper pan 29 of the core and coil assembly with spacer 55 therebetween.

The domed tank bottom member 12 is similar rigidly connected to the core and coil assembly 21 by a threaded stud 58 (see FIG. 5) welded to a plate 59 disposed above lower pan 30 and protruding through the axial opening in an annular metallic spacer 60 positioned between lower pan 30 and bottom member 12 and engaged within the internal threads in a nut 61 welded to the exterior of tank bottom member 12. Stud 58 is welded to nut 61 after assembly to prevent leakage of oil from the tank. The round shell 10 and domed cover 11 and tank bottom member 12 provide maximum mechanical strength against deformation of the tank, and inasmuch as domed cover 11 and tank bottom member 12 are rigidly afiixed to the core and coil assembly 21, minimum flexing and deformation of the transformer walls occurs due to internal pressure variations resulting from thermal changes of the transformer oil.

During manufacture the secondary bushings 33 are first assembled to the tank bottom member 12 having the foot 16 secured thereto. After the laminations 23 of the two magnetic cores 22 are linked with the coil 26, the backto-back cores 22 are framed in the lower and upper pans 30 and 29. The stud 58 on plate 59 is then inserted through the axial opening in spacer 60 and bottom member 12, nut 61 is threaded on stud 58, and the eye terminals 39 on secondary leads 40 are secured by nuts 41 to the conductor stud 34 of the secondary bushings 33. The core and coil assembly so assembled to tank bottom member 12 is subjected to vacuum and heat to remove moisture from the core and coil assembly. In a separate assembly operation cover 11 is welded to cylindrical shell 10 and one high voltage bushing 46 is secured to cover 11. The assembly of shell 10 and cover 11 is then positioned above the core and coil assembly 21 and the conductor of primary cable 47 extending from high voltage bushing 46 connected to a high voltage lead from the primary winding. Shell 10 having cover 11 welded thereto is then assembled over the core and coil assembly 21 and welded to the depending flange 19 on tank bottom member 12. Lifting eyenut 56 is then threaded on stud 52, tightened and welded to cover 11 and stud 52.

The transformer tank is then filled through filling plugs 64 (see FIG. 2) on cylindrical shell 10 with C. transformer oil 51 under negative pressure and sealed olf under vacuum. Preferably the core and coil assembly 21, the tank, and the oil are preheated, the oil is de-gassed, and the tank is filled under vacuum and sealed while hot so that when the unit cools the tank is still under vacuum and is filled with transformer oil 51 and no air cushion exists within the tank. When the unit cools, the internal pressure within the tank decreases still further. When the transformer is in service at ambient temperature, heating of the oil during operation of the transformer expands the oil until its volume is substantially equal to that of the tank, and consequently no appreciable positive internal pressure is exerted against the Walls of the tank during operation. Further, the circular shape of the shell 10 and the dome shape of cover 11 and tank bottom member 12 provide maximum mechanical strength against deformation of the tank.

In an alternative method of construction the transformer tank may be filled with cold oil and and then the entire oil-filled transformer heated to the desired temperature before the tank is sealed.

While only a single embodiment of the invention has been illustrated and described, many modifications and variations thereof will be readily apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such modifications and variations which are within the true spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hermetically sealed distribution transformer comprising, in combination, a tank having a circular metallic sidewall member welded to and closed at its upper and lower ends by outwardly domed metallic cover and bottom members respectively, a liquid dielectric within said tank, a transformer core and coil assembly immersed in said dielectric within said tank including a magnetic core linked by transformer primary and secondary windings and a unitary frame within said tank embracing the upper and lower portions of said core and coil assembly, and means rigidly connecting said frame to the central portion of said outwardly domed cover and bottom members for staying and preventing deformation of said cover and bottom members in both the inward and outward directions as a result of internal pressure changes within said tank.

2. A transformer in accordance with claim 1 wherein the interior of said tank is under a negative pressure relative to atmospheric when said transformer is out of service and said liquid dielectric has substantially the same volume as and fills said tank when said liquid dielectric is heated during operation of said transformer.

3. A transformer in accordance with claim 2 and including a plurality of secondary insulating bushings mounted on said bottom member and having conductor means extending therethrough connected to the secondary winding of said core and coil assembly.

4. A transformer in accordance with claim 3 and including a hanger bracket afiixed to said sidewall member and wherein said secondary bushings are positioned adjacent said hanger bracket and are approximately equidistant from said sidewall member.

5. A transformer in accordance with claim 4 wherein said hanger bracket depends below said bottom member and including a depending foot affixed to said bottom member in spaced relation to said hanger bracket and cooperating therewith to support said transformer in an upright position when said bracket and foot are rested on a horizontal surface.

6. A transformer in accordance with claim 5 wherein said cover member has an opening therein and including an upwardly extending suport ring afiixed to said cover member in surrounding relation to said opening and a high voltage insulating bushing extending through said opening and including a central conductor and a cylindrical body of insulating material surrounding said central conductor and having a circumferential flange above said support ring provided with a depending portion radially outward from and surrounding and being affixed to said support ring, said central conductor being embedded axially within said cylindrical body.

7. A transformer in accordance with claim 6, wherein said cylindrical body is cast of insulating resin and said central conductor is a length of high voltage cable molded 5 within said cylindrical body and said support ring has external threads and said depending portion of said cylindrical body has internal threads engaging said external threads on said support ring.

S. A hermetically sealed distribution transformer in accordance with claim 1 wherein each of said means rigidly connecting said frame to said cover and bottom members includes a pair of mating threaded members one of which is affixed to said frame and the other of which is aifixed to said central portion of said member and including spacer means disposed between said frame and said central portion in surrounding relation to one of said threaded members.

9. A transformer in accordance with claim 1 wherein said frame includes upper and lower hollow pans fitting over the upper and lower portions of said core and coil asembly respectively and elongated members within said tank joining said upper and lower pans together, and said means rigidly connecting said frame to said cover and bottom members engage said upper and lower pans.

10. A transformer in accordance with claim 9 wherein said means for staying and preventing deformation of said cover and bottom members includes spacer means between said upper and lower pans and said central portion of said domed cover and bottom members.

11. A transformer in accordance with claim 9 and including a lifting eye member aflixed to said means rigidly connecting said upper pan to said cover member.

12. A transformer in accordance with claim 10 wherein said means for staying and preventing deformation of said cover and bottom members includes threaded studs connected to said upper and lower pans extending through apertures in said spacer means and engaging female threaded means on said cover and bottom members.

13. A transformer in accordance with claim 12 wherein said means for staying and preventing deformation of said cover and bottom members includes a pair of plates integral with said threaded studs, one of said plates being disposed beneath said upper pan and the other being disposed above said lower pan.

14. A transformer in accordance with claim 13 and including a lifting eyenut on said cover member aflixed to the threaded stud which is integral with the plate disposed beneath said upper pan.

References Cited UNITED STATES PATENTS 1,034,929 8/1912 Reyndens et al. 33694 XR 1,912,389 6/1933 Smith 33694 2,065,662 12/1936 De Viney 336- XR 2,506,431 5/1950 Perret et al. 174-18 2,567,412 9/1951 Van Ryan 174-18 XR 3,097,346 7/1963 Horelick et al 33692 XR 3,234,493 2/ 1966 Zwelling et a1 33694 3,249,903 5/1966 Clark 336 XR 3,314,030 4/1967 Mallett et al 174l8 XR LEWIS H. MYERS, Primary Examiner T. I. KOZMA, Assistant Examiner US. Cl. X.R. 

